Pure YAG and rare earth-doped YAG ultra-fine particles with suitable morphology were obtained from a novel synthesis process by employing supercritical water. The synthesis process includes two steps including precursor precipitation and hydrothermal treatment in supercritical water system. The precursor was prepared by using yttrium nitrate, aluminum nitrate, rare earth nitrate and ammonium hydrogen carbonate aqueous solution as the starting materials. The YAG particles synthesized were mono-dispersed, featuring spherical or polyhedron shape with the size ranging from 100 nm to 500 nm. Factors influencing the properties of the final products were investigated in details. Structure characterization, morphology observation of the products were analyzed through XRD, SEM (scanning electron microscope) and other characterization techniques, respectively. (C) 2009 Elsevier B.V. All rights reserved.